We have seen very high populations of striped cucumber beetles on squash, pumpkins, cantaloupe, watermelon and other cucurbits over the last few weeks. These populations at times have reached over 20-30 beetles per plant. If a spray was missed or plants were not thoroughly covered with an insecticide application the beetles would soon consume that unprotected area very rapidly (Fig. 1). This area is often times the base of the plant. This is especially true if the cucurbits are sprayed with an air-blast sprayer. While air-blast sprayers do a good job of covering leaves with material, they often do not do a great job of covering the base of a plant and heavy feeding can occur (Fig. 2). The feeding can lead to plants being girdled by beetles or can lead to bacterial wilt infection—even though the leaves of the plant show almost no feeding. This feeding by the beetles also opens the base of the stem to infection from soil organisms and greater rates of Fusarium and bacterial soft rots are possible. When beetle populations are this high the base of the plant, even more so than the foliage, needs to be protected from heavy feeding.

Figure 1. Two squash leaves fed upon heavily by striped cucumber beetles because of the lack of good spray coverage.

I talk about this every year it seems, but I still see cucumber beetle and squash bug problems at the base of growers’ cucurbit plants. So far this has been a ‘good’ year for striped cucumber beetle and squash bug populations in just about every cucurbit field. Some fields have been hit particularly hard with beetles causing 5-10% plant loss due just to their feeding. The biggest problem with these pests, and why control sprays have not worked well, is that they are consistently hiding at the base of the plant where they are feeding on the stem. Most of the time we look for the foliage damage to tell us how well our spray program is working. Sprayers are set up usually to cover a lot of leaf canopy and do not do a very good job of putting chemical along the base of the stem. This stem feeding can be severe enough on small plants that either pest alone could cause some wilting, but with both feeding on this relatively small area of the stem they are causing considerable damage (Fig. 1). Even on larger plants the feeding can still cause significant damage (Fig. 2). It is hard enough to kill squash bug adults with a good cover spray, but when only small amounts of spray are reaching them on the lower stem they will not be controlled. Often it is possible to walk by plants and even inspect them and still see no beetles or squash bugs, as they will stay down at the base of the plant and only move when the base is exposed. In a couple fields about 10% of the plants were wilting (Fig. 3) due to squash bug and cucumber beetle feeding. These pictures are from a squash field but the same problem is occurring in watermelon and cantaloupe fields with both striped cucumber beetles and squash bugs feeding at the base of a plant. Growers need to check to see if this type of feeding is occurring in their fields and if so insecticide applications (pyrethroids such as Asana, Warrior, etc.) must be directed at the base of the plant.